This invention relates to a method and an apparatus for controlling the operation of weaving looms.
In the past, it has been proposed to produce a synchronization signal at a predetermined time during each weaving cycle of a loom by means of a suitable mechanical, electrical, or magnetic device in order to set the timing of the operation of the various operating elements of a loom on the basis of the synchronization signal. For example, mechanical and electrical systems to stop the loom at a predetermined angular position have been known.
The known mechanical system includes a cam, which makes one complete rotation during each one weaving cycle of the loom and is in operative contact with a lever. When a signal which requires an electric motor for driving a crank shaft of the loom to stop rotation, is applied to the device, the lever operates to bring a handle into a position, in which a clutch disposed between the motor and the crank shaft is disengaged and a brake is applied, thereby stopping operation of the loom. However, such a mechanical system can not be conveniently applied to a high speed loom, since not only is it of a relatively complex structure, but also its mechanical components would necessarily involve time delays in functioning.
One example of the known electrical systems is illustrated in FIG. 10, from which it is understood that a synchronization signal is produced every weaving cycle of the loom as shown at waveform (a). Assuming that a breakage of a yarn, such as a warp yarn, weft yarn, or selvage yarn occurs, a yarn breakage detector develops a yarn breakage signal as shown at waveform (b), which requires the operation of the loom to stop. Thereafter, a timer is energized, as shown at waveform (c), at the same time as the development of the first synchronization signal after the stop requirement signal has been produced. After a predetermined period of time during which the timer is on, that is, at a time point A, a motor stop and brake on signal is produced as shown at waveform (d) and the brake is put on, thus causing the loom to stop its rotation at a time point B or a predetermined angular position. It is therefore understood that in such a known electrical system the time point A, at which the brake begins to operate, is determined by determining both the time point B and the brake stopping time (B-A), and the time period between the time point C at which the associated synchronization signal issues and the time point A is alloted to operation of the timer. Therefore, in the case where the stop requirement signal is developed during a time period which corresponds in length to the time difference (A-C) and during which the timer would be energized if the stop requirement signal issues prior to said time period, the timer can not be energized until the next synchronization signal issues. That is, during the weaving cycle during which the stop requirement signal is developed, the loom stopping operation does not commence, only after said weaving cycle. In that case, even if the brake is so designed as to provide an increased brake force enabling braking to be completed within one weaving cycle of the loom, the loom stopping operation would not be effected within the same weaving cycle as that during which the stop requirement signal is developed. Thus, it is understood that no matter how much the brake force is increased, the time necessary to stop the loom at the desired angular position after the occurrence of the stop requirement signal can not be decreased.
Furthermore, the afore-mentioned known electrical system exhibits a disadvantage when the loom is operated intermittently or continuously at low speed. That is, in those circumstances, since the rotation of the loom is slow and its speed is not constant, while the preset time of the timer is always constant, the loom can not be stopped at the desired angular position. Also furthermore, when it is necessary to stop the loom at different angular positions in accordance with the cause for the stop requirement, such as a warp yarn and a weft yarn breakage, the known electrical system must include synchronization signal generators corresponding in number to the number of the causes for the stopping of the loom.
Meanwhile, where the weft yarn detector is of a photoelectric type, a timing of operation thereof has to be preset in order to prevent mulfunction thereof, i.e., to prevent the detector from detecting something other than a weft yarn. Since the timing of operation of the weft yarn detector is generally different from those of other operating elements of the loom, an additional synchronization signal generator must be provided which comprises a combination of a rotary member rotatable in synchronization with the rotation of the loom and a weft yarn sensing unit of a photoelectric or magnetic type.
It is understood from the foregoing that since the device for presetting the timing of operation in the aforementioned known electrical system comprises the combination of the timer and the synchronization signal generator generating one synchronization pulse signal every weaving cycle of the loom, when it is desired to control operating elements of which timings of operation differ from each other, the known electric system must include a plurality of presetting devices corresponding in number to the operating elements. Also, the known electrical system necessarily involves a time delay, which is longer than at least the preset time of the timer, between the issuing of the stop requirement signal and commencement of the loom stopping operation.